Xiao-Bao Yang

Bio: Xiao-Bao Yang is an academic researcher from South China University of Technology. The author has contributed to research in topics: Materials science & Boron. The author has an hindex of 10, co-authored 17 publications receiving 2438 citations. Previous affiliations of Xiao-Bao Yang include City University of Hong Kong.

Water‐Soluble Fluorescent Carbon Quantum Dots and Photocatalyst Design

Abstract: Carbon nanostructures are attracting intense interest because of their many unique and novel properties. The strong and tunable luminescence of carbon materials further enhances their versatile properties; in particular, the quantum effect in carbon is extremely important both fundamentally and technologically. Recently, photoluminescent carbonbased nanoparticles have received much attention. They are usually prepared by laser ablation of graphite, electrochemical oxidation of graphite, electrochemical soaking of carbon nanotubes, thermal oxidation of suitable molecular precursors, vapor deposition of soot, proton-beam irradiation of nanodiamonds, microwave synthesis, and bottom-up methods. Although small (ca. 2 nm) graphite nanoparticles show strong blue photoluminescence (PL), definitive experimental evidence for luminescence of carbon structure arising from quantum-confinement effects and size-dependent optical properties of carbon quantum dots (CQDs) remains scarce. Herein, we report the facile one-step alkali-assisted electrochemical fabrication of CQDs with sizes of 1.2– 3.8 nm which possess size-dependent photoluminescence (PL) and excellent upconversion luminescence properties. Significantly, we demonstrate the design of photocatalysts (TiO2/CQDs and SiO2/CQDs complex system) to harness the use of the full spectrum of sunlight (based on the upconversion luminescence properties of CQDs). It can be imagined that judicious cutting of a graphite honeycomb layer into ultrasmall particles can lead to tiny fragments of graphite, yielding CQDs, which may offer a straightforward and facile strategy to prepare high-quality CQDs. Using graphite rods as both anode and cathode, and NaOH/EtOH as electrolyte, we synthesized CQDs with a current intensity of 10–200 mAcm . As a reference, a series of control experiments using acids (e.g. H2SO4/EtOH) as electrolyte yielded no formation of CQDs. This result indicates that alkaline environment is the key factor, and OH group is essential for the formation of CQDs by the electrochemical oxidation process. Figure 1a shows a trans-

Photo and pH stable, highly-luminescent silicon nanospheres and their bioconjugates for immunofluorescent cell imaging.

Abstract: We report a novel kind of oxidized silicon nanospheres (O-SiNSs), which simultaneously possess excellent aqueous dispersibility, high photoluminescent quantum yield (PLQY), ultra photostability, wide pH stability, and favorable biocompatibility. Significantly, the PLQY of the O-SiNSs is as high as 25%, and is stable under intense UV irradiation and in acidic-to-basic environments covering the pH range 2-12. To our best knowledge, it is the first example of water-dispersed silicon nanoparticles which possess both high PLQY and robust pH stability suitable for broad utility in bioapplications. Furthermore, the O-SiNSs are readily conjugated with antibody, and the resultant O-SiNSs/antibody bioconjugates are successfully applied in immunofluorescent cell imaging. The results show that the highly luminescent and stable O-SiNSs/antibody bioconjugates are promising fluorescent probes for wide-ranging bioapplications, such as long-term and real-time cellular labeling.

Transparent and flexible selenium nanobelt-based visible light photodetector

Abstract: We report a synthesis of single-crystal [001] oriented selenium nanobelts (SeNBs) through a simple vacuum evaporation at 250 °C. The width and thickness of the SeNBs are in the range of 100–800 nm and 20–90 nm, respectively. I–V analysis of an individual SeNB based field effect transistor (FET) reveals typical p-type electrical conduction. The hole mobility and concentration are respectively estimated to 0.63 cm2 (V s)−1 and 9.35 × 1016 cm−3. The p-type electrical characteristics can be explained by the surface termination model, according to which, H- or OH- termination can induce a defect level slightly above the valance band maximum (VBM). A fully transparent and flexible visible light photodetector assembled on a polyethylene terephthalate (PET) substrate shows a high sensitivity to visible light illumination, with sensitivity and conductive gain as high as 3.27 × 104 A W−1 and 6.77 × 104 respectively. Furthermore, the device also exhibits a stable performance and good reproducibility under different bending conditions. The high-performance visible light photodetector would enable application opportunities in future flexible and transparent electronics.

Surface passivation and transfer doping of silicon nanowires.

Abstract: One-dimensional nanomaterials are expected to play a key role in future nanotechnology, in addition to providing model systems to demonstrate the unique characteristics of nanoscale effects. Silicon nanowires (SiNWs) in particular are potentially very attractive, given the central role of Si in the semiconductor industry, and are being extensively studied. A SiNW for use in nanodevices is composed of three sections: SiNW core, surface passivant, and adsorbates or interface compounds. A unique way to modulate the transport properties of SiNWs could depend on the individual sections. Volume doping is a conventional method to control conductivity. In volume doping, impurity atoms are introduced into the crystal lattice in the SiNW core by an in situ process during growth, 5] ion implantation, and related methods. However, volume doping for SiNWs has inherent disadvantages, such as poor controllability and destructive processing. Interestingly, the conductivity of amorphous Si films was found to be sensitive to adsorbates, which indicates the importance of the surface of low-dimensional systems in determining the electrical properties of materials. The large surface-to-volume ratio of SiNWs could potentially be important in influencing their transport properties. Its effect could be exploited through SiNW functionalization. Indeed, recent studies of SiNW-based chemical sensors 10] find strong conductivity responses of SiNWs to environmental conditions. Other relevant observations include conductivity modification by adsorbents in the hydrogen-terminated (H-terminated) surfaces of diamond crystals, conductivity determination by surface states in nanoscale thin silicon-on-insulator (SOI) systems, and conductivity enhancement of hydrogenated SiNWs in air and recovery through vacuum or gas purging. Thus, the possibility to modulate the conductivity of SiNWs using surface effects is promising. The ease of such an approach, economically and nondestructively, would offer a unique advantage for use of SiNWs in device fabrication. However, the success of this approach will depend on its controllability and repeatability, and most importantly on the understanding of the mechanisms of the surface effect on SiNWs. Herein, we present a new doping approach, namely surface passivation doping, built on the known surface transfer doping and based on extensive first-principles theoretical investigations and systematic experiments on the surface effects of SiNWs. We also elucidate the involved mechanism and provide better understanding to predetermine the electrical properties of nanomaterials. Surface hydrogen termination is a natural consequence of the hydrogen fluoride treatment of SiNWs. To reveal the role of hydrogen termination in conductivity, we first performed first-principles calculations based on density functional theory (DFT) with an efficient SIESTA code. 15] We adopted popularly used basis sets with double zeta and polarization functions and the Lee–Yang–Parr functional of generalized gradient approximation. We collected atomic charges from a Mulliken population analysis based on DFT calculation, which gave a reasonable charge distribution, as verified using a water molecule ( 0.46 j e j charges on the oxygen atom and 0.23 j e j charges on each hydrogen atom). Interestingly, we obtained extra charges of 0.06 j e j on average on each surface hydrogen atom of the H-terminated SiNWs (H-SiNWs). Clearly, the partial negative charge on the hydrogen atom is due to the higher electronegativity of the hydrogen atom compared to that of the silicon atom (2.2 vs. 1.9). This partial electron transfer from the silicon core to the surface hydrogen is negligible for bulk silicon but is significant for surface-dominated SiNWs whose carrier concentration could be considerably modified, as is estimated below. Assuming each surface silicon atom is terminated by two hydrogen atoms on average, we can calculate the total number of electrons trapped on the terminating hydrogen atoms using Equation (1):

The formation of boron sheet at the Ag(111) surface: From clusters, ribbons, to monolayers

Abstract: Boron (B) sheet has been intently studied and various candidates with vacancies have been proposed by theoretical investigations, including the possible growth on metal surface. However, a recent experiment (Science 350, 1513, 2015) reported that the sheet formed on the Ag(111) surface was a buckled triangular lattice without vacancy. Our calculations combined with High-Throughput screening and the first-principles method demonstrate a novel growth mechanism of boron sheet from clusters, ribbons, to monolayers, where the B-Ag interaction is dominant in the nucleation of boron nanostructures. We have found that the simulated STM image of the sheet with 1/6 vacancies in a stripe pattern is in better agreement with the experimental observation, which is energetically favored during the nucleation and growth.

Carbon quantum dots and their applications

Abstract: Fluorescent carbon nanoparticles or carbon quantum dots (CQDs) are a new class of carbon nanomaterials that have emerged recently and have garnered much interest as potential competitors to conventional semiconductor quantum dots. In addition to their comparable optical properties, CQDs have the desired advantages of low toxicity, environmental friendliness low cost and simple synthetic routes. Moreover, surface passivation and functionalization of CQDs allow for the control of their physicochemical properties. Since their discovery, CQDs have found many applications in the fields of chemical sensing, biosensing, bioimaging, nanomedicine, photocatalysis and electrocatalysis. This article reviews the progress in the research and development of CQDs with an emphasis on their synthesis, functionalization and technical applications along with some discussion on challenges and perspectives in this exciting and promising field.

Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging

Abstract: Fluorescent carbon-based materials have drawn increasing attention in recent years owing to exceptional advantages such as high optical absorptivity, chemical stability, biocompatibility, and low toxicity. These materials primarily include carbon dots (CDs), nanodiamonds, carbon nanotubes, fullerene, and fluorescent graphene. The superior properties of fluorescent carbon-based materials distinguish them from traditional fluorescent materials, and make them promising candidates for numerous exciting applications, such as bioimaging, medical diagnosis, catalysis, and photovoltaic devices. Among all of these materials, CDs have drawn the most extensive notice, owing to their early discovery and adjustable parameters. However, many scientific issues with CDs still await further investigation. Currently, a broad series of methods for obtaining CD-based materials have been developed, but efficient one-step strategies for the fabrication of CDs on a large scale are still a challenge in this field. Current synthetic methods are mainly deficient in accurate control of lateral dimensions and the resulting surface chemistry, as well as in obtaining fluorescent materials with high quantum yields (QY). Moreover, it is important to expand these kinds of materials to novel applications. Herein, a facile and highoutput strategy for the fabrication of CDs, which is suitable for industrial-scale production (yield is ca. 58%), is discussed. The QY was as high as ca. 80%, which is the highest value recorded for fluorescent carbon-based materials, and is almost equal to fluorescent dyes. The polymer-like CDs were converted into carbogenic CDs by a change from low to high synthesis temperature. The photoluminescence (PL) mechanism (high QY/PL quenching) was investigated in detail by ultrafast spectroscopy. The CDs were applied as printing ink on the macro/micro scale and nanocomposites were also prepared by polymerizing CDs with certain polymers. Additionally, the CDs could be utilized as a biosensor reagent for the detection of Fe in biosystems. The CDs were prepared by a hydrothermal method, which is described in the Supporting Information (Figure 1a; see also the Supporting Information, Figure S1). The reaction was conducted by first condensing citric acid and ethylenediamine, whereupon they formed polymer-like CDs, which were then carbonized to form the CDs. The morphology and structure of CDs were confirmed by analysis. Figure 1b shows transmission electron microscopy (TEM) images of the CDs, which can be seen to have a uniform dispersion without apparent aggregation and particle diameters of 2–6 nm. The sizes of CDs were also measured by atomic force microscopy (AFM; Figure S2), and the average height was 2.81 nm. From the high-resolution TEM, most particles are observed to be amorphous carbon particles without any lattices; rare particles possess well-resolved lattice fringes. With such a low carbon-lattice-structure content, no obvious D or G bands were detected in the Raman spectra of the CDs (Figure S3). The XRD patterns of the CDs (Figure 1c) also displayed a broad peak centered at 258 (0.34 nm), which is also attributed to highly disordered carbon atoms. Moreover, NMR spectroscopy (H and C) was employed to distinguish sp-hybridized carbon atoms from sp-hybridized carbon atoms (Figure S4). In the H NMR spectrum, sp carbons were detected. In the C NMR spectrum, signals in the range of 30–45 ppm, which correspond to aliphatic (sp) carbon atoms, and signals from 100–185 ppm, which are indicative of sp carbon atoms, were observed. Signals in the range of 170– 185 ppm, which correspond to carboxyl/amide groups, were also present. In the FTIR analysis of CDs, the following were observed: stretching vibrations of C OH at 3430 cm 1 and C H at 2923 cm 1 and 2850 cm , asymmetric stretching vibrations of C-NH-C at 1126 cm , bending vibrations of N H at 1570 cm , and the vibrational absorption band of C=O at 1635 cm 1 (Figure S5). Moreover, the surface groups were also investigated by XPS analysis (Figure 1d). C1s analysis revealed three different types of carbon atoms: graphitic or aliphatic (C=C and C C), oxygenated, and nitrous (Table S1). In the UV/Vis spectra, the peak was focused on 344 nm in an aqueous solution of CDs. In the fluorescence spectra, CDs have optimal excitation and emission wavelengths at 360 nm and 443 nm, and show a blue color under a hand-held UV lamp (Figure 2a). Excitation-dependent PL behavior was [*] S. Zhu, Q. Meng, Prof. J. Zhang, Y. Song, Prof. K. Zhang, Prof. B. Yang State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University Changchun, 130012 (P. R. China) E-mail: byangchem@jlu.edu.cn

Graphene-based semiconductor photocatalysts

Abstract: Graphene, a single layer of graphite, possesses a unique two-dimensional structure, high conductivity, superior electron mobility and extremely high specific surface area, and can be produced on a large scale at low cost. Thus, it has been regarded as an important component for making various functional composite materials. Especially, graphene-based semiconductor photocatalysts have attracted extensive attention because of their usefulness in environmental and energy applications. This critical review summarizes the recent progress in the design and fabrication of graphene-based semiconductor photocatalysts via various strategies including in situ growth, solution mixing, hydrothermal and/or solvothermal methods. Furthermore, the photocatalytic properties of the resulting graphene-based composite systems are also discussed in relation to the environmental and energy applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation and photocatalytic disinfection. This critical review ends with a summary and some perspectives on the challenges and new directions in this emerging area of research (158 references).

Carbon nanodots: synthesis, properties and applications

Abstract: Carbon nanodots (C-dots) have generated enormous excitement because of their superiority in water solubility, chemical inertness, low toxicity, ease of functionalization and resistance to photobleaching. In this review, by introducing the synthesis and photo- and electron-properties of C-dots, we hope to provide further insight into their controversial emission origin (particularly the upconverted photoluminescence) and to stimulate further research into their potential applications, especially in photocatalysis, energy conversion, optoelectronics, and sensing.